Not applicable.
(1) Field of the Invention
The present invention relates to mechanical fastening systems and more particularly to such systems including a metal core and a resinous exterior.
(2) Brief Description of the Prior Art
Carbon to metal joints have generally been considered to be galvanically incompatible. Because carbon is an efficient cathode, it has heretofore been necessary to completely isolate carbon from metals in a marine environment. Use of adhesives only reduces reliability. Composite materials such as carbon fiber reinforced plastics (CFRP) and fiberglass reinforced plastics (FRP) are susceptible to failure from bearing stress on mechanical fasteners.
The prior art discloses a number of ways of attaching reinforced polymer components to metal components of a structure.
U.S. Pat. No. 4,033,243 to Kirrish et al., for example, discloses a novel fastener assembly for use in attaching a composite panel section or the like to a frame section. The fastener assembly comprises a first member for engagement in a bore formed in said frame section, said member including an enlarged, tamper-proof head engaging the exterior surface of said frame section and means for preventing rotation relative to said frame sections; and a second member being disposed in a coaxial bore formed in said panel, and having an enlarged head for engagement with said panel, said head including a drive tool engaging means. In addition, the aforementioned first member engaged with said frame section, includes a seal means for attaining a watertight joint when said respective head portions are brought into clamped engagement with said frame and panel sections.
U.S. Pat. No. 4,310,273 to Kirrish discloses a novel fastener assembly for use in securing a frame section to a composite panel or the like, said fastener assembly being dielectrically insulated from said frame section to prevent galvanic action. The fastener assembly is comprised of a bolt member adapted for engagement in a bore formed in said frame section, said bolt member having an enlarged head portion including annular axially facing groove means, and an annular axially extending non-conductive elastomeric gasket member disposed in said groove means, and a nut member having an enlarged head portion for engagement with said bolt member. The nut member is disposed in a coaxial bore formed in said composite panel and engaged with said bolt member also disposed in said bore. Upon assembly, the gasket member is clamped between the frame and the enlarged head on the bolt and is deformed axially and radially. That is, the gasket is extruded into the space between the bolt member and the frame to insulate said bolt member from said frame section. In addition, the aforementioned gasket member provides a watertight joint when said bolt and nut members are brought into clamping engagement with said frame and panel sections.
U.S. Pat. No. 4,902,180 to Gauron discloses a fastener element that is ejection molded from an engineering resin of a type that will bond to potting resin used for securing the fastener element within a cavity formed within a panel of composite material. The fastener element includes flow control disks spaced apart along a stem portion between end portions. Flats are formed on opposite sides of the flow control disks. Below fill and vent openings. Resin introduced into the fill hole travels down to the bottom of the cavity and around the fastener element and fills the cavity from the bottom up, so that the presence of resin at the vent opening will indicate that the cavity has been filled with resin and does not include an airspace or void.
U.S. Pat. No. 5,169,180 to Villoni et al. discloses a fluid conducting connector for use in water connections particularly water heater connectors. The connector assembly is designed for mating connection to a galvanized nipple for reduction of galvanic corrosion between dissimilar metal connections. An insulator sleeve is seated within the connector to maintain separation between the galvanized nipple and the copper tube of the assembly. The connector assembly includes an internally threaded female connector mounted to the copper tube for connection to the nipple. The insulator sleeve includes a tubular body and a radial flange. The body of the sleeve extends partially into the copper tube while the flange seats within the female connector acting as a washer for the assembly.
U.S. Pat. No. 5,175,665 to Pegg discloses a lightning resistant composite structure, particularly for aircraft, in which a composite skin panel, for example of carbon fiber, is attached to an inner composite structure by one or more lightening resistant fastener assemblies. The fastener assembly is comprised of a nut and bolt, the bolt being in good conductive contact with a conductive sleeve engaging the skin panel and a nonconductive sleeve engaging the inner structure. The nut is contained within a capped nut assembly located to the undersurface of the inner structure. The nonconductive sleeve and the capped nut assembly isolate the inner structure from the effects of lightening strike, the conductive sleeve providing a high quality conductive interface between the bolt and the skin panel. By this means, adverse penetration of lightening current into the inner structure is prevented.
U.S. Pat. No. 5,807,051 to Heminger discloses an adhesive insert anchor including an anchor body and a screw member for insertion into a drilled hole in a substrate containing an adhesive. The anchor body further includes an integral friction segment and an adhesion segment. The friction segment includes an internally threaded cavity in which to receive the screw member and a knurled portion. The adhesion segment includes a cylindrical section and a plurality of saucer-shaped buttons positioned along its length ending with a terminal button. The buttons on the adhesion segment provide greater surface area for contact between the adhesive and the anchor. The friction segment has an external diameter substantially the same as the diameter of the hole drilled in the substrate, thereby providing a friction fit between the anchor body and the walls of the substrate hole. The external diameter of the adhesion segment is smaller than the external diameter of the friction segment so that when the anchor body is inserted into the hole in the substrate, there is space between the adhesion segment and the walls of the hole which is completely filled by adhesive so as to securely bond the anchor body with the substrate. The friction fit of the friction segment maintains the adhesion segment of the anchor body a proper distance from the bottom of the substrate hole and provides for light-duty loading of the anchor while the adhesive cures. Upon installation, the adhesion segment is twisted into the hole, thereby agitating the adhesive, which disrupts the substrate dust remaining on the walls of the hole. This allows proper adhesion between the adhesive and the concrete. With the addition of a sleeve, the anchor can be used in overhead applications. An alternate embodiment includes the addition of an insulator fitted to the anchor body to form the friction segment. The insulator being electrically nonconductive and the adhesive being electrically conductive to form a dielectric adhesive insert anchor.
A need still exists, however for am improved way to attach a reinforced polymer element to metal elements of a structure.
It is an object of the present invention to provide an improved mechanical fastening system for attaching reinforced polymer elements to other elements of a structure and a method for its installation.
It is a further object of the present invention to mechanically fasten galvanically incompatible materials without providing an electrical path or contact area and reduce bearing loads especially in carbon fiber reinforced plastics (CFRP) to metals.
These and other objects are met by the present invention, which is a galvanically isolated mechanical fastening system that comprises
an exterior first section having a first transverse bore. The system also includes an exterior second section having a second transverse bore, wherein said second transverse bore is aligned with said first transverse bore. There is also an interior third section having a third transverse aperture. This third section is interposed between said first section and said second section and said third transverse bore is aligned with said first and second transverse bores. A fastener is positioned in the first, second and third transverse bore and is fixed to the first section. A polymeric material is positioned in the third section between the fastener and the peripheral wall of the third section.